High-pressure fuel pump

ABSTRACT

A high pressure fuel pump includes a cylinder having a pressurizing chamber and a plunger inserted into the cylinder. The plunger is axially reciprocated by a lifter to pressurize fuel in the pressurizing chamber. A seal member encompasses a portion of the plunger that is projected from the cylinder. The seal member disconnects a cylinder side space surrounded by the seal member from a lifter side space outside the seal member. The seal member has an annular lip portion that contacts a peripheral surface of the plunger, and the annular lip portion has a pair of lips separated from each other in an axial direction of the plunger. An axial distance between the lips is greater than a stroke of the plunger. As a result, fuel does not enter the lifter side space, and lubricating oil does not enter the cylinder side space.

BACKGROUND OF THE INVENTION

The present invention is related to a high pressure pump forpressurizing and supplying fluid, and more particularly, to a highpressure pump that is optimal for pressurizing and supplying fuel to afuel injection valve of a vehicle engine.

Japanese Laid-Open Publication No. 8-68370 discloses a high pressurefuel pump used for a vehicle engine. The high pressure fuel pump has acylinder, a plunger that is inserted into the cylinder, and a lifterthat moves the plunger axially direction with respect to the cylinder.As the plunger reciprocates, the plunger pressurizes fuel in apressurizing chamber, which is defined in the cylinder, and dischargesthe fuel from the pressurizing chamber.

The lifter contacts one end of the plunger that is projected from thecylinder. The lifter is slidably supported by a pump housing. Agenerally cylindrical seal member is attached to the cylinder so as tosurround the portion of the plunger that is projected from the cylinder.The seal member has an annular lip portion defined at its distal end.The annular lip portion contacts an outer peripheral surface of theplunger. The seal member prevents fuel, which leaks from thepressurizing chamber through a clearance between the cylinder and theplunger from mixing with lubricating oil that lubricates the lifter.

FIGS. 4(a) and 4(b) are cross sectional views of a plunger 43 and a sealmember 41. Although not shown, a cylinder is positioned upward of FIGS.4(a) and 4(b), and a lifter is positioned downward of FIGS. 4(a) and4(b). The seal member 41 disconnects a cylinder side space (the spacesurrounded by the seal member 41) from a lifter side space (the spaceoutside the seal member 41). The lip portion 42 of the seal member 41has an upper lip 42 a and a lower lip 42 b that are spaced from eachother in the axial direction of the plunger 43. The upper lip 42 aprevents fuel L1 collected on the peripheral surface of the plunger 43from entering the lifter side space. The lower lip 42 b prevents thatlubricating oil L2 invades into the cylinder side space. Therefore, fueland lubricating oil are prevented from mixing.

When the plunger 43 moves in a direction projecting out of the cylinder,that is, when the plunger 43 moves downward in FIG. 4(a), the fuel L1collected on the peripheral surface of the plunger 43 is removed by theupper lip 42 a. The removed fuel L1 is stored in the cylinder side spaceand prevented from entering the lifter side space. On the other hand,when the plunger 43 moves in a direction entering the cylinder, that is,when the plunger 43 moves upward in FIG. 4(a), the lubricating oil L2collected on the peripheral surface of the plunger 43 is removed by thelower lip 42 b and prevented from entering the cylinder side space.

However, it is difficult to completely remove the fuel L1 and thelubricating oil L2 collected on the plunger 43 by the lip portion 42.Therefore, in the high pressure fuel pump of the above publication, themixing of the fuel and the lubricating oil is not sufficientlyprevented. When the fuel leaks into the lifter side space and mixes withthe lubricating oil, the lubricating oil is diluted and the liftercannot be lubricated sufficiently.

When the plunger 43 moves from the highest position shown in FIG. 4(a)to the lowest position shown in FIG. 4(b), the fuel L1′ that is notremoved by the upper lip 42 a temporarily enters the space between theupper lip 42 a and the lower lip 42 b and then passes by the lower lip42 b to leak into the lifter side space.

When the plunger 43 moves from the lowest position shown in FIG. 4(b) tothe highest position shown in FIG. 4(a), the lubricating oil that is notremoved by the lower lip 42 b temporarily enters the space between theupper lip 42 a and the lower lip 42 b and passes by the upper lip 42 ato leak into the cylinder side space.

As the stroke of the plunger 43 lengthens to increase the dischargedamount of the fuel, the leakage amount of the fuel and the lubricatingoil increases.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a high pressure pumpfor that guarantees prevention of fluid leakage from one of two spaces,which are disconnected by a seal member, into the other one of the twospaces.

To achieve the above object, a high pressure pump includes a cylinderhaving a pressurizing chamber. A plunger is inserted in the cylinder.The plunger is axially reciprocated with a predetermined stroke topressurize fluid in the pressurizing chamber. The plunger has aprojected portion projected from the cylinder. A drive member drives theprojected portion to reciprocate the plunger. A seal member encompassesthe projected portion. The seal member has an annular lip portion thatcontacts a peripheral surface of the projected portion. The annular lipportion has a pair of lips separated from each other in an axialdirection of the plunger. An axial distance between the lips is greaterthan the stroke of the plunger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a high pressure fuel pump accordingto an embodiment of the present invention.

FIGS. 2(a) and 2(b) are enlarged cross sectional views showing a lipportion of a seal member of FIG. 1.

FIG. 3 is a graph showing the relationship of a leakage amount withrespect to the difference between the distance between lips and aplunger stroke.

FIGS. 4(a) and 4(b) are cross sectional views showing a seal member of aprior art high pressure fuel pump.

DETAILED DESCRIPTION

A high pressure pump according to the present invention embodied in ahigh pressure fuel pump 11 that is applied to a vehicle engine will nowbe discussed with reference to FIGS. 1 to 3. Although not shown in thedrawings, the high pressure fuel pump 11 of FIG. 1 pressurizes fuel,which is sent from a fuel tank by a feed pump, to supply the fuel to adelivery pipe.

The high pressure fuel pump 11 has a housing 12 and a cylinder 13, whichis arranged in the housing 12. The cylinder 13 has a pressurizingchamber 14. A bracket 15 is fixed to the lower end of the housing 12 bya plurality of bolts 16. The cylinder 13 is supported by the bracket 15and the housing 12. The cylinder 13 has a bore 13 a that communicateswith the pressurizing chamber 14 and extends axially. A plunger 17 isinserted in the bore 13 a in an axially movable manner.

A guide cylinder 15 a extends downward from the bottom surface of thebracket 15. A lifter 18, which is cylindrical and has a closed bottom,serves as a drive member is coupled and is fitted in the guide cylinder15 a in an axially movable manner. A basal end of the plunger 17, whichprojects from the cylinder 13, contacts an inner bottom surface of thelifter 18. A camshaft 22 of an engine is arranged below the lifter 18. Aretainer 20 is engaged to a with the basal end of the plunger 17. Aspring 21 is arranged between the retainer 20 and the bracket 15 in acompressed state. The spring 21 presses the basal end of the plunger 17toward the inner bottom surface of the lifter 18 and urges the lifter 18toward the camshaft 22.

The camshaft 22 has a cam (not shown) for driving a discharge valve ofthe engine and a drive cam 23 for driving the plunger 17. The drive cam23 has two cam noses 23 a separated from each other by an angularinterval of 180 degrees. The spring 21 presses and the lifter 18 againstthe cam surface of the drive cam 23.

The cylinder 13 has a fuel supply passage 24 that communicates with thepressurizing chamber 14. An electromagnetic spill valve 25 is arrangedin the fuel supply passage 24.

The electromagnetic spill valve 25 has an electromagnetic solenoid. Whenvoltage is not applied to the electromagnetic solenoid, theelectromagnetic spill valve 25 opens the fuel supply passage 24 tocommunicate the fuel supply passage 24 with the pressurizing chamber 14.In this state, when the plunger 17 is lowered and projected from thecylinder 13, low pressure fuel that is sent from a fuel tank (not shown)by the feed pump is drawn into the pressurizing chamber 14 via the fuelsupply passage 24. When voltage is applied to the electromagneticsolenoid, the electromagnetic spill valve 25 closes the fuel supplypassage 24 and disconnects the fuel supply passage 24 from thepressurizing chamber 14. In this state, when the plunger 17 is liftedand moved into the cylinder 13, the volume of the pressurizing chamber14 decreases, which in turn, pressurizes the fuel in the pressurizingchamber 14.

A high pressure fuel passage 26 extends from the pressurizing chamber 14through the cylinder 13 and the housing 12. A check valve 27 is arrangedin the high pressure fuel passage 26. When the fuel pressure in thepressurizing chamber 14 exceeds a predetermined value, the check valve27 is opened, and the high pressure fuel is supplied from thepressurizing chamber 14 to a delivery pipe (not shown) via the highpressure fuel passage 26. The high pressure fuel is further distributedfrom the delivery pipe to each fuel injection valve of the engine.

When the engine is driven, the drive cam 23 is rotated integrally withthe camshaft 22 and the lifter 18 is reciprocated axially with respectto the guide cylinder 15 a in accordance with the profile of the drivecam 23. The plunger 17 is reciprocated axially in cooperation with thelifter 18. As shown by the double-dashed line in FIG. 1, when the drivecam 23 is positioned at rotation position R1, the lifter 18 is moved tothe lowest position where the lifter 18 is closest to the camshaft 22.In this state, the distal end 17 a of the plunger 17 is moved to thelowest position where the distal end 17 a is farthest from thepressurizing chamber 14 and the volume of the pressurizing chamber 14 ismaximized.

When the drive cam 23 is rotated in the counterclockwise direction inFIG. 1 from rotation position R1 to rotation position R2, one of the camnoses 23 a lifts the lifter 18. This projects the distal end 17 a of theplunger 17 into the pressurizing chamber 14 and gradually decreases thevolume of the pressurizing chamber 14. When the drive cam 23 is furtherrotated from rotation position R2 to rotation position R3, one of thecam noses 23 a moves the lifter 18 to the highest position. In thisstate, the distal end 17 a of the plunger 17 moves to the highestposition where the volume of the pressurizing chamber 14 is minimized.In this manner, a fuel pressurizing stroke is performed when the drivecam 23 lifts the plunger 17.

In the pressurizing stroke, unless voltage is applied to theelectromagnetic solenoid of the electromagnetic spill valve 25, the fuelin the pressurizing chamber 14 is not discharged to the delivery pipeand spilled into the fuel tank via the fuel supply passage 24. Ifvoltage is applied to the electromagnetic solenoid at a proper timingduring the pressurizing stroke, the electromagnetic spill valve 25closes the fuel supply passage 24. Therefore, the fuel in thepressurizing chamber 14 is pressurized as the plunger 17 moves upward.The pressurized fuel pushes and opens the check valve 27 to bedischarged into the delivery pipe. The fuel discharge amount is adjustedby changing the closing timing of the electromagnetic spill valve 25during the pressurizing stroke. The electromagnetic spill valve 25 iscontrolled by an electronic control unit (not shown) arranged in theengine in accordance with running condition of the engine.

When the drive cam 23 is further rotated in the counterclockwisedirection in FIG. 1 from rotation position R3, the urging force of thespring 21 gradually lowers the lifter 18 and the plunger 17 from thehighest position. When the drive cam 23 is rotated to rotation positionR1, the lifter 18 and the plunger 17 reaches the lowest position again.In this manner, when the drive cam 23 allows the plunger 17 to belowered, a fuel intake stroke is performed.

When the lifter 18 and the plunger 17 reaches the highest position, theelectronic control unit stops applying voltage to the electromagneticsolenoid of the electromagnetic spill valve 25. Therefore, theelectromagnetic spill valve 25 remains opened during the intake stroke.The fuel sent from the fuel tank by the feed pump is drawn into thepressurizing chamber 14 via the fuel supply passage 24.

Afterward, the above-described pressurizing stroke and intake stroke areexecuted repeatedly and a proper amount of high pressure fuel isdischarged from the high pressure fuel passage 26 to the delivery pipe.

As shown in FIG. 1, a coupling cylinder 13 b extends downward from thelower end of the cylinder 13 and through the bracket 15. The couplingcylinder 13 b forms part of the bore 13 a. A generally cylindrical sealmember 28 is fitted to and around the coupling cylinder 13 b. The sealmember 28 encompasses the portion of the plunger 17 projected from theplunger 17. The seal member 28 disconnects an inner space, or cylinderside space A1, which is encompassed by the seal member 28 from an outerspace, or a lifter side space A2, which is defined outside the sealmember 28. A slight amount of the fuel in the pressurizing chamber 14leaks into the cylinder side space A1 through a clearance between thewall of the bore 13 a and the peripheral surface of the plunger 17.Lubricating oil for lubricating the lifter 18 exists in the lifter sidespace A2. The seal member 28 prevents the fuel in the cylinder sidespace A1 from mixing with the lubricating oil in the lifter side spaceA2.

As shown in FIGS. 1, 2(a), and 2(b), the seal member 28 has a metalsupport cylinder 29 and a rubber seal 30, which is arranged along theinner surface of the support cylinder 29. An annular lip portion 31defined at the lower end of the rubber seal 30 contacts the peripheralsurface of the plunger 17. The lip portion 31 has an upper lip 31 a anda lower lip 31 b, which are separated from each other in the axialdirection of the plunger 17. The edge of the upper lip 31 a and the edgeof the lower lip 31 b are pressed against the peripheral surface of theplunger 17.

In this embodiment, the lip portion 31 is designed and formed so that anaxial distance S1 between the upper lip 31 a and the lower lip 31 b isgreater than stroke S2 of the plunger 17. More specifically, thedistance S1 is the axial distance between the portion of the upper lip31 a contacting the peripheral surface of the plunger 17 and the portionof the lower lip 31 b contacting the peripheral surface of the plunger17.

When the plunger 17 is not moving, the upper lip 31 a prevents the fuelL1 collected on the peripheral surface of the plunger 17 from enteringthe lifter side space A2, as shown in FIG. 2(a). The lower lip 31 bprevents the lubricating oil L2 collected on the peripheral surface ofthe plunger 17 from entering the cylinder side space A1. Therefore, thefuel and the lubricating oil are prevented from mixing.

In the intake stroke, that is, when the plunger 17 is moves downward asviewed in FIG. 2(a), the fuel L1 collected on the peripheral surface ofthe plunger 17 is removed by the upper lip 31 a. The removed fuel L1 isheld in the cylinder side space A1 and prevented from entering thelifter side space A2. On the other hand, in the discharge stroke, thatis, when the plunger 17 is moved upward as viewed in FIG. 2(a), thelubricating oil L2 collected on the peripheral surface of the plunger 17is removed by the lower lip 31 b and prevented from entering thecylinder side space A1.

When the plunger 17 is moved downward in the intake stroke, the fuel L1that is not removed by the upper lip 31 a remains on the peripheralsurface of the plunger 17, as shown in FIG. 2(b). However, as describedabove, in this embodiment, the axial distance S1 between the upper lip31 a and the lower lip 31 b is larger than the stroke S2 of the plunger17. Therefore, when the plunger 17 moves from the highest position shownin FIG. 2(a) to the lowest position shown in FIG. 2(b), the residualfuel L1′ does not pass by the lower lip 31 b to enter the lifter sidespace A2. The residual fuel L1′ only enters the space between the upperlip 31 a and the lower lip 31 b.

Although not shown in the drawings, when the plunger 17 moves upward inthe discharge stroke, the lubricating oil that is not removed by thelower lip 31 b remains on the peripheral surface of the plunger 17.However, in the same manner as described above, when the plunger 17moves from the lowest position shown in FIG. 2(b) to the highestposition shown in FIG. 2(a), the residual lubricating oil does not passby the upper lip 31 a to enter the cylinder side space A1. The residuallubricating oil only enters the space between the upper lip 31 a and thelower lip 31 b.

As described above, in this embodiment, the fuel L1′ that is not removedby the upper lip 31 a does not enter the lifter side space A2. Further,the lubricating oil that is not removed by the lower lip 31 b does notenter the cylinder side space A1. This prevents fuel and lubricating oilfrom being mixed. Accordingly, dilution of the lubricating oil with thefuel is prevented, and satisfactory lubrication of the lifter 18 ismaintained.

FIG. 3 is a graph showing the relationship between the leakage amount ofthe fuel and the lubricating oil with respect to the difference betweenthe distance S1 and the plunger stroke S2 (S1−S2). The result shown bythe graph was obtained through experiments. As apparent from the graph,when the difference (S1−S2) is greater than a predetermined positivevalue, that is, when the distance S1 is greater than or equal to theplunger stroke S2 by a predetermined value, the leakage amount of thefuel and the lubricating oil is significantly decreased.

The seal member 28 has the metal support cylinder 29 and the rubber seal30, which is arranged on the inner surface of the support cylinder 29.The support cylinder 29 faces the lifter side space A2 and is notexposed to the fuel in the cylinder side space A1. Therefore, even iflow grade fuel that contains moisture exists in the cylinder side spaceA1, the metal support cylinder 29 does not rust.

The present invention may be embodied as follows.

The seal member 28 may not be attached to the housing 12 or the bracket15 instead of the cylinder 13.

The support cylinder 29 may be embedded in the rubber seal 30.Alternatively, contrary to an arrangement shown in FIG. 1, the rubberseal 30 may be arranged around the support cylinder 29.

The application of the present invention is not limited to the highpressure fuel pump shown in FIG. 1 and but may be applied to a varietyof high pressure fuel pumps. For example, in the pump of FIG. 1, theclosing timing of the electromagnetic spill valve 25 during thepressurizing stroke is changed to adjust the fuel discharge amount.However, the present invention may be embodied in a high pressure fuelpump that adjusts the fuel discharge amount by changing the openingtiming of the electromagnetic valve during the intake stroke.

The present invention may be also be embodied in a high pressure pumpthat pressurizes fluid other than fuel.

What is claimed is:
 1. A high pressure pump comprising: a cylinderhaving a pressurizing chamber; a plunger inserted in the cylinder,wherein the plunger is axially reciprocated with a predetermined stroketo pressurize fluid in the pressurizing chamber, the plunger having aprojected portion projected from the cylinder; a drive member fordriving the projected portion to reciprocate the plunger; and a sealmember encompassing the projected portion, wherein the seal member hasan annular lip portion that contacts a peripheral surface of theprojected portion, the annular lip portion having a pair of lipsseparated from each other in an axial direction of the plunger, whereinthe seal member disconnects an inner side space surrounded by the sealmember from an outer side space outside the seal member, fluid thatleaks from the pressurizing chamber exists in the inner side space, andlubricating oil that lubricates the drive member exists in the outerside space, and wherein each lip has a contact portion that contacts theperipheral surface of the projected portion, and an axial distancebetween the contact portions of the two lips is greater than the strokeof the plunger by a predetermined value so that a section of theperipheral surface of the projected portion that contacts one of thelips does not contact the other one of the lips when the plungerreciprocates.
 2. The high pressure pump according to claim 1 wherein theseal member has a metal support cylinder and a rubber seal arranged onan inner surface of the support cylinder, and the annular lip portion isarranged on one end of the rubber seal.
 3. The high pressure pumpaccording to claim 1, wherein the cylinder has a coupling cylinder, theplunger projects out of the cylinder from the coupling cylinder, and theseal member is fitted to the coupling cylinder so as to surround thecoupling cylinder.
 4. A high pressure pump comprising: a cylinder havinga pressurizing chamber; a plunger inserted in the cylinder, wherein theplunger is axially reciprocated with a predetermined stroke topressurize fluid in the pressurizing chamber, the plunger having aprojected portion projected from the cylinder; a drive member fordriving the projected portion to reciprocate the plunger; and a sealmember encompassing the projected portion, wherein the seal member hasan annular lip portion that contacts a peripheral surface of theprojected portion, the annular lip portion having a pair of lipsseparated from each other in an axial direction of the plunger, whereinthe seal member disconnects an inner side space surrounded by the sealmember from an outer side space outside the seal member, fluid thatleaks from the pressurizing chamber exists in the inner side space, andlubricating oil that lubricates the drive member exists in the outerside space, and wherein each lip has a contact portion that contacts theperipheral surface of the projected portion, and an axial distancebetween the contact portions of the two lips is greater than the strokeof the plunger by a predetermined value so that a section of theperipheral surface of the projected portion that contacts one of thelips does not overlap a section of the peripheral surface of theprojected portion that contacts the other one of the lips when theplunger reciprocates.
 5. The high pressure pump according to claim 4,wherein the seal member has a metal support cylinder and a rubber sealarranged on an inner surface of the support cylinder, and the annularlip portion is arranged on one end of the rubber seal.
 6. The highpressure pump according to claim 4, wherein the cylinder has a couplingcylinder, the plunger projects out of the cylinder from the couplingcylinder, and the seal member is fitted to the coupling cylinder so asto surround the coupling cylinder.